By FREDERIC J. FROMMER
WASHINGTON — Andy Pettitte took the stand Tuesday in the Roger Clemens perjury trial and described how he grew up admiring the star pitcher he is expected to testify against.

Under questioning from a prosecutor, Pettitte also said that Clemens became a mentor to him when the two were teammates on the New York Yankees.

Pettitte, who is mounting a comeback with the Yankees, is expected to testify that Clemens told him he had used human growth hormone. Clemens has said that Pettitte "misremembers" the conversation. The two were close friends.

Clemens is accused of lying to Congress when he denied in a 2008 deposition and hearing that he had used steroids or HGH.

The trial broke for lunch before Pettitte got to the meat of his testimony. The government used its first questions to try to establish the relationship between the two men.

"We hit it off immediately," Pettitte said in a slow, Texas drawl.

Pettitte's testimony came after Clemens' lawyer plowed ahead with a line of questions challenging the merits of the congressional investigation into drug use among baseball players, despite a judge's warning that doing so could open the trial to government evidence of widespread use of steroids and human growth hormones in baseball.

Clemens lawyer Rusty Hardin asked how each of the questions that Clemens faced back then, which led to the alleged false statements, could have possibly lead to legislation — one of the justifications for the congressional investigation into drugs in baseball.

In an often combative cross-examination, the government's first witness, congressional staffer Phil Barnett, told Hardin that the questions and answers could have informed legislation, such as classifying HGH as a controlled substance. Barnett was majority staff director for the House Oversight and Government Reform Committee when that panel held the 2008 hearing. But Barnett said that no legislation was passed as a result of the hearing.

Late Monday, U.S. District Judge Reggie Walton said if the Clemens defense team continued its attack on the 2008 congressional hearing, government prosecutors should be allowed to present a "larger picture" of why the hearing took place.

Walton asked the government to show him the kind of information it wants to present. A prosecutor gave a hint at the end of Monday's session — with the jury out of the room — dropping the names of admitted drug users among major league players, such as Chuck Knoblauch and Jose Canseco. The defense fears this could taint Clemens with guilt-by-association.

Prosecutors said it's a necessary rebuttal to questions raised by Clemens' lawyer about the motive for the hearing.

Prosecutors are using Barnett to try to establish that Congress was within its bounds in holding the hearing two months after Clemens was named in the 2007 Mitchell Report to the Commissioner of Baseball on drug use in the sport. The government has maintained that it was important for Congress to learn whether the report was accurate, in part because of concerns about steroids and HGH as a public health issue.

Hardin has complained that the congressional hearing was "nothing more than a show trial." Determining whether Clemens was telling the truth when he denied the report's claims, he said, "is not a legitimate role for Congress."

Hardin Monday raised the issue of whether Clemens' testimony at the hearing was truly voluntary — suggesting that Clemens might have been subpoenaed had he not agreed to appear. But Barnett wouldn't concede that the pitcher would have been subpoenaed had he declined the committee's invitation; he said such a move was not automatic.

With Barnett on the stand, the government played portions of Clemens' televised testimony at the February 2008 hearing as well as an audiotape of the deposition that preceded it.

"Let me be clear: I have never used steroids or HGH," Clemens said confidently in the videotape of the hearing.